The present disclosure relates to a carbon brush of an electric motor and a method for producing the carbon brush.
There exists an electric motor in which an armature shaft of an armature, around which a coil is wound, is pivotally rotatably supported by a yoke to which a permanent magnet is installed. A commutator is provided to the armature shaft. The coil, which is wound around the armature, is electrically connected to the commutator. The coil is supplied with power when the commutator is slidingly in contact with a brush to which an external power source is connected. The armature thus rotates as the coil is excited.
When the brush is made of carbon, such as a graphite brush, there exist problems. While such a brush slides along the commutator, electrical abrasion and mechanical abrasion on sliding-contact surfaces (sliding surfaces) occur toward the commutator. A spark discharge is also caused because of deterioration in a rectification property. As a result, the durability is deteriorated. Therefore, such abrasion and deterioration in the rectification property should be inhibited so that the durability can be enhanced.
Regarding the graphite brush, carbon coatings are formed on sliding-contact surfaces by air around the commutator or air in air holes of the brush. Such carbon coatings may contribute to the inhibition of abrasion and deterioration in the rectification property. However, the carbon coating formation is strongly affected by the conditions of the sliding-contact portions between the brush and the commutator based on the surrounding environment of the motor when it is used, such as temperature and humidity. When an atmospheric temperature around the sliding-contact portions is high, for example, carbon coatings are impaired. A condition of the sliding-contact between the brush and the commutator is then deteriorated. Sparks are also increasingly generated. As a result, the durability is deteriorated.
A proposed graphite brush of an electric motor is thus structured so as to be capable of controlling the conditions of formation of carbon coatings in accordance with the conditions in which the electric motor graphite brush is used. A rectification property and a durability of the electric motor may thus be improved (see Japanese Published Unexamined Patent Application No. 2004-173486, for example). As the proposed method, the brush is formed through successive steps. Natural graphite is used as a raw material; a binder, an additive, and copper are added thereto; and press molding and a sintering process are carried out, thereby forming the brush. After that, liquid that has a high boiling point than water is impregnated into air holes that are formed inside the formed brush. Accordingly, carbon coatings can be formed at a higher temperature, a temperature of a sliding-contact portion is greater than or equal to 100 degrees Celsius; and abrasion can be reduced between the brush and the commutator in high temperature regions. As a result, the durability may be enhanced.